Chlorine dioxide is primarily used in pulp bleaching, but there is a growing interest of using it also in other applications such as water purification, fat bleaching or removal of organic materials from industrial wastes. Since chlorine dioxide is not storage stable it must be produced on-site.
Production of chlorine dioxide in large scale is usually performed by reacting alkali metal chlorate or chloric acid with a reducing agent and recovering chlorine dioxide gas. Such processes are described in, for example, U.S. Pat. No. 5,091,166, 5,091,167 and 5,366,714, and EP patent 612886.
Production of chlorine dioxide in small scale, such as for water purification applications, can also be done from alkali metal chlorate and a reducing agent but requires somewhat different processes, such as those described in U.S. Pat. No. 5,376,350 and 5,895,638.
The above small scale processes include feeding alkali metal chlorate, hydrogen peroxide and a mineral acid to a reactor, in which chlorate ions are reduced to form chlorine dioxide. In these processes it has now been found favourable to use a premixed solution of alkali metal chlorate and hydrogen peroxide as a feed. However, such solutions are not storage stable, particularly due to decomposition of hydrogen peroxide, but there is also a risk for a reaction between the hydrogen peroxide and the chlorate to form chlorine dioxide. The decomposition of hydrogen peroxide is particularly rapid in the presence of ferrous- and/for chromium ions, which may be introduced as in impurity in alkali metal chlorate or be released from storage containers of steel.